Wide band coupling system



July 25, 1939. H. A. WHEELER WIDE BAND COUPLING SYSTEM 5 Sheets-Sheet 2 Filed April 22, 19:38

INVENTOR H LD A.wHEEL R ATTORNEY July 25, 1939- H. A. WHEELER WIDE BAND, GOUPLING SYSTEM Filed April 22. 1958 5 Sheets-Sheet 3 INVENTOR you) A. WHEELER B ATTORNEY July 25, 1939- H. A. WHEELER 2,167,134

WIDE BAND COUPLING SYSTEM Filed April 22, 1938 5 Sheets-Sheet 4 c g Gm E -Cm-HI T g T k T g T m.. R Halo i i i 4i- KW 0 C 0 'E 1: -fmk mg n., malo.

.e E i j -fmc MTW l u C C C h g -mk =f",1 mm Ro FIGJOO.

i f T F\G.l l. aNvENTO HAROLD A. WHEELER ATTORNEY July 25, 1939. H. A. WHEELER 2,167,134

WIDE BAND COUPLING SYSTEM Filed April 22, 1938 5 Sheets-Sheet 5 ATTORNEY hama July 2s, 1939 2,167,134

UNITED STATES PATENT OFFICE WIDE BAND COUPLING SYSTEM Harold A. Wheeler, Great Neck, N. Y., assigner to llaleltinc Corporation, a corporatlon nl Delaware Application April 22, 1938. Serial No. 203,505

17 Claims. (Cl. 178-44) This invention relates generally t Coupling tively easy to build up the impedance in the circuit systems and particularly t0 swirling systems of less capacitance and relatively diillcult in the including a pair of terminals between which there circuit oi' more capacitance. Substantially uniis substantial conductance and susceptance and form over-all response may be obtained by causing between' which il' is deslld t0 build up a high imthe impedance to increase towards the cutoi! ire- 5 pedance or high admittance which is substanquency in the circuit oi' less capacitance and to tially constant over a wide range of frequencies. decrease in the same direction in the circuit of The invention is of particular utility in a network more capacitance. Coupling arrangements of the comprising one or more coupling systems coupled prior art have not used component coupling syslo in cascade in which the impedance variation of tems coupled in cascadein which the component l0 one or more of the coupling systems varies in a coupling systems have complementary impedance manner complementary to that of another or variations and in which the maximum mean value others of the coupling systems over a wide range of impedance or admittance is maintained in the o! frequencies, whereby a predetermined or subcomponent coupling systems over a wide frel5 stantially uniform over-al1 responseisobtained. quency range. Also, the ed'ect of substantial ll In many coupling arrangements, it is desirable shunt conductance or series-resistance in such to build up a substantially uniform impedance coupling circuits has not been compensated. having the largest possible mean value over a wide In coupling two consecutive tubes of unequal range oi' frequencies across terminals having concapacitance. it is sometimes advantageous to use 20 ductance and susceptance in parallel therewith, a. network which is not adapted for unequal ca- 20 or to maintain maximum admittance over the pacitance and, therefore, has nonuniform rerange between terminals having inductance and spouse between unequal values oi capacitance. resistance in series therewith; that is, itis de- Even if the two tubes have equal capacitance, the sirable to maintain approximately the limiting most convenient network may be one which gives mean value of impedance, eithermaximum or nonunlform response between two tubes of equal 25 minimum. between the terminals over the wide capacitance. The prior art has not shown the range o! frequencies. For instance, in the design combination of such arrangements in different of vacuum-tube amplifiers to pass a wide range stages which have complementary variations of of frequencies. it is desirable to build up across 'a responsiveness in order to permit the maximum condenser, comprising the inherent capacitance of freedom of design. 30 the tube circuits to be coupled. the maximum im- It is an object of the invention to provide a pedance that can be maintained substantially unicoupling system comprising reactance and reform over the operating frequency range of the sistance wherein a maximum mean value oi' imampliiier. Such impedance characteristics are pedance or admittance is maintained over a wide required of the coupling systems of the amplier frequency range. 35 and the value of the impedance which can be It is another object of the invention to provide maintained over a given frequency range is lima. coupling system having maximum impedance ited by the inherent capacitance and conductance over a wide frequency range for use between two oi the tube circuits to be coupled. ,Prior art cousuccessive tubes of a vacuum-tube amplifier.

40 pling arrangements designed for this purpose It is still another object of the invention to pro- 40 have only approximated the desired results and vide a composite network including several couthe effect of resistance inherent in such amplier pling systems coupled in cascade and having circuits has generally been neglected. different response characteristics in which the Also, it is frequently desirable to obtain from a mean impedances of the coupling systems are composite network comprising several component maintained within predetermined limits and in 45 coupling systems coupled in cascade, a response which the over-all response of the composite netcharacteristic having a predetermined variation work varies in a predetermined manner over the with frequency over a wide range oi' frequencies, frequency range. while maintaining the maximum mean value of In accordance with one embodiment of the inimpedance or admittance across the component vention, a signal-translating system for operation 50 coupling systems. For example, in a wide band over a range of frequencies comprising one or amplifier including, in two stages coupled in casmore pairs of terminals between one pair oi' which cade. two tubes of widely diilerent types, the in there is effectively substantial reactance and subherent capacitance of the circuits of the two tubes stantial resistance. both tending to limit the remay be greatly diflerent. In this case it is relaspense of the system over its range. A dead-end 55 filter is provided having an image impedance over the range coupled to one ofthe pairs of terminals. the filter comprising only a part of the reactance associated with the said pair of terminals as a terminal mid-element of the filter and an impedance termination coupled to the dead end of the lter proportioned substantially to match the lmage impedance of the filter over its range. The reactive constants of the dead-end iilter are so proportioned relative to the reactance and resistance associated with the said pair of terminals and the operating frequency range that the impedance between the said pair of terminals over said range is substantially uniform and approximately the limiting value that can be maintained between the said terminals over the range. In one embodiment of the invention. a dead-end iiiter ls utilized in each of two or more component coupling systems of a composite network to procure, in the component coupling systems, impede ance characteristics or response characteristics which vary in a predetermined manner with respect to each other. preferably compiementarily. over a. wide range of frequencies, thereby to provitdie a predetermined over-all response characteris c.

In other embodiments of the invention, a deadend filter is so proportioned and coupled to a terminal circuit of the coupling system that a substantially constant impedance is obtained. over a wide frequency range. across the terminal circuit, which may also comprise appreciable resistance effectively in parallel or in series.

Other modifications of the dead-end filter of the invention are described and claimed in applicant's applications Serial No. 203.596. Serial No. 203,597, and Serial No. 203,598, iiled concurrently with the present application while a general circuit arrangement for maintaining uniform impedance across terminals comprising inductance associated therewith and tending to limit the response of the system over a wide range of frequencies is described and broadly claimed in applicants cope'nding application Serial No. 161,017. led August 26, 1937, all assigned to the same assignee as the present applica-tion.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specincation taken in connection with the accompanying drawings, in which Figs. l and 3 are simplied or equivalent circuit diagrams utilized to explain the general theory of the invention; Figs. 2 and 4 are graphs illustrating certain of the operating characteristics oi the circuits of Figs. l and 3; Figs. tia-45e, inclusive, are circuit diagrams utilized to explain the general theory of the invention with reference to a illter circuit comprising shunt capacitance across one or more sets of terminals; Figs. 6er-6c, inclusive. are circuit diagrams utilized to explain the general theory of the invention with reference to a lter circuit comprising inductance in series with one or more sets of terminals; Figs. 'la-8c, inclusive, are circuit diagrams utilized to explain the general theory of the invention with reference to a lter circuit in which the input and output circuits have reciprocal impedance properties: Fig. 9 is a circuit diagram utilized to explain the general theory of the invention with reference to a band-pass lter; Figs. 10a-10e, inclusive, are circuit diagrams of a number of practical fourars-1,1

terminal low-pass iilter circuits in accordance with the invention; Fig. 11 is a circuit diagram of a four-terminal band-pass filter circuit in accordance with the invention: Fig. 12 is a circuit diagram illustrating a manner of coupling three vacl uuxn tubes in successive stages of a vacuum-tube amplifier by means of nlter circuits in accordance with the invention; Fig. 13 illustrates a band-pass coupling system comprising a filter circuit of the invention for coupling two vacuum-tube amplifiers; while Fig. i4 is a circuit diagram of filter circuits in accordance with the invention utilised to couple a push-pull power ampliiler to an antenna circuit.

lhe principles of the theoretical relations underlying the invention are described most slmply by reference to a nondisslpative wave iilter of the constant-Ic type. This nlter may be assumcd to have an innitc number of sections or to be terminated with its image impedance to give the same en'ect. The input impedance oi' such a lter is uniform over the pass bands if the input ter-*- mination is full-series or full-shunt as dlstin. gulshed from the usual mid-series or mid-shunt termination. The input impedance is the iterative impedance measured in series with a-full-series arm or in parallel with a full-shunt arm. as dis.v tinguished from the conventional image .impedance measured at mid-series or mid-shunt. This input impedance may be regarded as a two-terminal coupling impedance, the remainder of the filter serving merely as a dead-end supplementary network utilired to secure the desired uniform impedance.

Any such iiiter of nite total band width can be arranged to include directly across its full-shunt arm. a capacitance of the value l C=2/RA 'fll in which R is the mid-band image impedance and Au is 21 times the total width of the pass bands. The uniform full-shunt iterative impedance across the capacitance C has the magnitude R=2ICA (2) This relationship expresses the theoretically maximum value of impedance that can -be .maintained across the capacitance C throughout frequency bands oi total width A. In the case of a simple low-pass filter, the value of R is twice the reactance of the capacitance C at the cutoi! frequency.

The problem reciprocal to building up the im-4 pedance across a capacitance is building up the admittance through an inductance. A nlter can be arranged to include directly in series with all the other elements of its series arm, an inductance of the value L=2R'/Aw (3) The uniform full-series iterative impedance through the inductance L has the magnitude R'=LAw/2 (4) This relationship expresses the theoretically minimum value of impedance that can be maintained through an inductance L over the frequency bands of total width Au. In the case of a simple lowpass ilter, this value is half the reactance of the inductance L at the cutoif frequency. The speciilcation will not be generalized to include the derivations of expressions relating to maintaining 7g a given value of admittance through an inductance, because all the relations hereinafter given can be applied to this problem by the analogy which appears in the preceding formulae.

The image impedance of a filter of the type u llii aromas as to the impedance across a capacitance or the admittance through en inductance. The phase characteristic is that of anali-sectional a constent-l: filter. A more general analysis is given hereinafter with reference to a simple low-pass filter. without any loss of generality in the foregoing concepts.

Referring now to the drawings. Fig. l shows the basic filter circuit in simplified form. the nlter, per se, being represented schematically at 1 and having input terminals l and output terminals t. 'I'he input termination Cm oi filter 1 is a mid-shunt element and the input image impedance Zi follows the constant-k characteris-y tic. The output' termination'of filter .1 is either mid-series or mid-shunt and its image impedance zi' preferably follows an 1ra-derived characteristic to match closely the output load resistanpe R. In developing the theoretical relations, this lmpedance matching is assumed to be exact in the` pass bands. since anyrequired degree of approximation is possible by means of multiple ml-derivatlons. V

For the sake of generality and clarity, the total capacitance C0 across the input terminals l may have any value and is divided in two parts, Cn comprising the mid-shunt capacitance termination of the nlter. and Cs the external added capacitance, thus, only a part of the total capacitance across terminals I is included in the illter as a mid-shunt element. The input impedance Z is. therefore, across the total shunt capaci-4 tance, Ce=Cm+C1a This impedance is to be built up with the aid oi' a dead'end filter acting merely as a passive auxiliary network.

The shunt capacitance Cm in the illter is the mid-shunt element of a terminal half-section. This half-section may be of m-derived type (m 1) or oi' constant-k type (m=1). since either type is available in a form whose mid-shunt termination presents the desired constant-lc image impedance Z1 across shunt capacitance Cm. In such a half-section. the value or the mid-shunt capacitance is in which e is 21de. where In is the cutoff frequency of the low-pass iliter. The external shunt capacitance Cn can have any value as determined by the choice of the parameter n in the formula The factor m+n) may have anyl positive value. One of the parts may be negative. since the parts do not have to exist separately. Negative Cn merely means that the total capacitance C is less' than the mid-shunt capacitance Cm of the filter. Equation (7) may also be' written as The image impedance Z| depends only on Re and we, not on Cm and m, because it always has the constant-k characteristic:

The Image impedance is resistive in the pass band, capacitive in the attenuation band, and infinite at cutoi! frequency. It is convenient to use the l parameter z=uloe to denote the relative frequency in subsequent expressions. The relative impedance of Ca and Zr in parallel is RJaHWQRJrI-*iiwm (u) This formula has a discontinuity at the cutoff frequency (:|:=l) wherethe Zi term of the denominator changes from real to imaginary. It is seen that the form of the impedance characteristic depends only on n Rocnfe (l from Equation (8) and does not depend on m=l|r.c..c (14) from Equation y(5). v

In the pass band v(:r: i). Z/Ro is complex and its nx l1 if (16) This is the same as the formula for a half-section m-type filter except that the m of the filter is replaced by the parameter n which determines the relative value of Cn. Ii n=1, it simplifies to In the attenuation band (:r l) Z/u is imaginary and its magnitude is Z 1 R -y/xT- l-i-xn (la) It has a lagging phase angle. b=zr2. These characteristics cannot be realized exactly because the output image impedance Zi' cannot match R0 outside the pass band. As the attenuation increases. this failure has less effect on the input impedance. Therefore. any degree of approximation to the theoretical characteristics outside the pass band can be realized with a suiilcient number of sections designed to secure adequate attenuation.

Fig. 2 shows the theoretical impedance characteristics for various values of the parameter n between i and +4. It is noted that the values +1 yield uniform impedancein the pass band. If the iliter has a constant-k whole section on the input side, so that m=l the values +1 and -1 for n correspond, respectively. to full-shunt and full-series termination. In the former case, the addition of Cn doubles the mid-shunt element, while in the latter case it cancels the mid-shunt element. The sign of the parameter n does not affect the magnitude of the impedance in the pass b and, but it does determine the sign .of the phase angle.

. Since only positive self-reactance elements can be realized'in a passive network, the value of m in the end half-section of a filter must be between 0 and +1. Since m-i-n must be positive. the value `ofen must be between -l and -i-w. Negative v frequency C. URM (20) which corresponds to Equation (i) Any change of the total capacitance, by changing the-value of a. causes an inverse change of the average impedance in the pass band, although its value Re at aero freuuenca' remains the same.

In the pass band. the impedance near the cutoil' frequency is determined mainly by the value of n. that is. by the external shunt capacitance Cn. The image impedance Zi having less elect.

the tolerance o! mismatching between Z1' and Rs at the tar end of the iilter becomes greater.

Also, this tolerance increases with n. The number ci sections in the iilter aects the number oi peaks and valleys inthe actual impedance curve o! Z, while the phase characteristics ailect their spacing along the frequency axis.

The general concepts utilised above to develop the expressions relating to low-pass iilters are generally valid tor filters having any number o! pass bands. The mid-shunt capacitance Cm may be supplemented by parallel branches to i'orm an impedance network of the form required in a constant-k shunt arm to give the required pass bands. C also may be supplemented and in this case the inside and outside shunt arms can still be merged into one. The generalized relation corresponding to Equation (10) is RsCnAw: n

in which A is the total width of the pass bands. Uniform impedance of magnitude Rs is secured in all pass bands ii' 11:1. It is secured with maximum shunt capacitance if also m=l. This terminal resistor Re across the dead end o! the. iilter. Dissipation in the iiiter has the eect ci smoothing out the impedance curve and rounding the discontinuity at the cutoil frequency.

which is not very detrimental in moderation.

Another source of dissipation is shunt conductance across the input terminals. that is. across the desired impedance Z. This may exist in substantiai amount and is detrimental because it limits the impedance that can be built up across a given shunt capacitance over a given frequency."

f iform impedance is obtained across maximum band.

Pig. 3 represents a low-pass network oi the.,

type of Fig. l. but having conductance Gsadded directly in shunt to the impedance Z. Its value relative to the terminating shunt conductanceI Gor-IIR@ delinea the parameter n':

an: nGs (22) me total shunt capacitance aisomay be expressedintermscilG.:

` C.=C+C.=(m+n)G-vlv (23) The initial value ci the impedance Z. at x=0. is

- The general expression corresponding to Equa tions (10) (2l) above is The impedance is complex at all frequencies and still has the discontinuity at the cutoi! frequency. In the pass band. the relative magnitude of the impedance is L z- ..1/(n'+1/1-x)1+xlnl The a lagging` phase angle In the attenuation band. the relative magnitude of the impedance is and the lagging phase angle is l1=terri-V+".,xs-Fl (30) nieoretically uniformV impedance over the pass bandsis' not possible, but the condition for approximate uniformity is obtained from Formula mi (2?) -by 'expanding into a series convergent in the pass band:

The coeiiicient of c* cancels out under the condition n=/l+n o'r n'=nl (32) leaving' only relatively small terms in the higher powers of :r:

At the cutoff frequency. the peak value is 'w//= 1.15 corresponding to n=l. The approximately unishunt capacitanceii" m=l., so Equation (25) becomes 1 l ZIICIWInJilJT-l-n- It is to be noted that "this ngure of merit decreases with increasing shunt conductance.

Fig. 4 shows a family of impedance `curves for various values of shunt conductance in terms of the parameter n'.- the value of nin each case being that required by Equation (82) for ap- 5 proximately uniform impedance. The gure in dicates some .advantages of the shunt conduce tance. The' peak at the cutoii'frequency can be used to compensate for the rounding effect oi' dissipation inthe filter and of mismatching at the far end oi' the filter. I

The low-pass two-terminal networks described above maybe utilized to maintain a limiting impedance (maximum impedance) across a capacitance element or a limiting impedance (maxim mum admittance) through an inductance ele ment. The former may be used to secure maximum voltage from a current-regulated generata'. such as a vacuum tube having large internal resistance and appreciable shunt capacitance. The

gg latter may be used to secure maximum current from a voltage-regulated generator, such as a moving coil having small internal resistance and appreciable series inductance. The capacitance or inductance is the total of both input'and output circuits.

,The dead-end filter of the invention also may be lutilised in a four-terminal network and each of the two terminal' devices, the generator and the load, may have either shunt capacitance or series inductance. 'Ihere are four permutations of such four-terminal networks. In general. each of the terminal devices is limited in performance, over a wide frequency band.- by either shunt susceptance or series reactance. A current-regulated generator or a voltage-responsive device have in common the property of small shunt conductance. and the limitation is imposed by Ishunt susceptance. A voltage-regulated generator or a current-responsive load have in common the property of small series resistance and the limitation' is imposed by series reactance.

'Ihe four-terminal networks of the invention employ the above recited principles for malntaining a predetermined impedance across vsusceptance, or a predetermined admittance through reactance, over a wide band of frequencies. The total susceptance or reactance of the circuits tobe coupled is divided into smaller component portions connected in different sections of a iilter. so that the impedance or admittance ofthe iilter is limited not by the total but by the greatest indivisible portion.

'Ihe four-terminal networks of the invention are best exemplified by separating the input and output devices in the filter, instead of connecting them directly in parallel or in series. Further benei'its may be obtained by further subdivision involving more than two pairs of terminals. For example, the capacitance to ground of connecting o leads or of a large grid condenser may be separated and may comprise a reactive element of another section of the illter.

Figs, 5a-8c. inclusive, are the bases of the theoretical explanation of four-terminal netv works. They are developed from low-pass filters but exemplify all filters having a nite total band width. The capacitive and inductive arms shown are. respectively, the parallel and series arms of low-pass filters. While a shunt conductance Gn or series resistance Rn is shown in the filters of Figs. 5a8c, inclusive, it will be understood that. under the principles outlined above, this resistance may be of such value as to have an inappreciable effect. in which case Ait can be neglected; or, by including the parameter n' in aromas l 5 the expressions involving the filter reactance elexnents, the filter can be so 'as to taks into account the Aeilect of this resistance or conductance.

Figs. 5dr-5c, inclusive. represent the develop- 5 ment of a filter for building up. a uniform impedance across susceptance. Fig. 5a is essentially a two-terminal network with the susceptance of a capacitance element Cn across its terminals. In Fig, 5a the relationships of Equations (5). (6). 10 and (7), given above. apply. The dead-end filter of Fig. 5a is assumed to be nondissipative. It is shown divided in two parts it and I i. which division is a basis for the analysis of the four-termina! networks. The dead-end filter il), ii may 15 correspond to that shcwnin Fig. 3, and similar circuit elements have been given identical reference numerals. Elements Cm' and Cm" are the respective mid-shunt condensers of parts iii and ii at their adjacent ends. The network i 0 is sup- 2o plied with input current In from a currentregulated generator (not shown). which develops across Zv the output voltagelih which is the same as the input voltage El across the generator ter- The part in of the dead-end alter is symmetrical" in that it has the same constant-Ic midshunt image impedance at both ends. This does not require symmetry of circuit arrangement 30- within the lter, and does not require any constent-Ic half-sections in the filter, although both w of these attributes may be present.` The part il of the dead-end filter has constant-k mid-shunt image impedance at the end coupled to part I0. 35 while at the opposite end it has'preferalzvly mderived in iage impedance assumed to match the terminal resistor Re over the pass band. At the Junction of parts II and i i, the mld-shunt capacitance elements have the values: 40

^ minals, though displaced in phase. Therefore.

the output voltage Ez can lust as well be obtained at the junctionas shown in Fig. 5b. It is then determined by the4 characteristics of both the 60 input impedance Z and the transfer impedance v of part lil of the filter:

I (as) v 65 in which (a4-ib) represents the attenuation in napiers and the phase lag in radians in the active portion il of the filter. Part Il is still inactive and functions only as a dead-end network to control the impedance. Ihe attenuation a is 70 assumed to be zere in the pass band.

The phase shift land attenuation obtained by making the part i0 of the filter active between input and output terminals may or may not be desired. but there is a definite advantage in that 75 the limitation on the impedance. imposed by the shunt capacitance is out in half by distributing the input and output capacitance between diilerent parts of the nlter. In a filter of given impedance and band width, this doubles the total capacitance permitted across the input and output circuits. Alternatively, if the total capacitance and band width are given, this ex pedient doubles the impedance that can be maintained uniform over the pass band.

The transier impedance given by Equation (38) is a reciprocal property of a four-terminal network.- Therefore, the network of I lig. 5b can be reversed as 'shown in Fig. 5c, while retaining its transfer characteristics unchanged. The dead end of the filter is changed over from the output side to the input side.

Figs. 6a, 6b. and 6c are reciprocaliy analogous to Figs.'5a, 5b, and 5c by interchange of concepts, such as current and voltage. impedance and admittance, susceptance and reactance. resistance and conductance. capacitance and inductance. shunt and series. etc., the dead-end nlter of the invention being. in this case. divided into parts I2 and II. In Pig. 8a the admittance Y. which is uniform over the pass band of the dead-end filter. is developed through the two inductance elements In and In in series. The former is regarded as the mid-series arm of the filter, per se, and the latter is regarded as an external auxiliary inductance element. but both are usually merged in a single inductance element denoted La Their values are Ln=mGnwei Ln='1t/'Goue (39) La=La+Ls=(m-in) /Gwe in which G=Y1IR is the mld-band" value of admittance Y (at aero frequency in the lowpass case). For uniform admittance, n=i.

The two-terminal network i2 is supplied with input voltage E1 from a voltage-regulated generator, which develops through Y the output current I: which is the same as the input current I1 from the generator:

Ia=I1=YEi (40) The filter is separated into parts i! and i3 with constant-k mid-series image impedance at the junction of thefparts, where the inductance elements have the values:

L.i'=m'/Gw: Lm"=m"/Ga (n) L'=L'+L"=(m'+m")/Gaw In the arrangement of Fig. 6b. the output ourrent In is obtained at the filter junction. It is determined by the characteristics oi both the input admittance Y and the transfer admittance of active part I! of the lter:

I: I1!| -itl-Ye l* (42) The limitation onthe input admittance. imposed by the total series inductance oi input and output circuits. is cut in half relative to Fig. 6a.

Figs. 7a, '1b. 7e, and Figsaa. so, and sc show thedevelopment of coupling networks in which the input and output circuits have reciprocal properties. that is, shunt susceptance and series reactance, or vice versa` 'Ihe active part of each filter has reciprocal symmetry" of image characteristics; that is, it has mid-shunt image impedance at one end and mid-series image admittance at the other end. both being of the constant-k form. Since they are reciprocal. the quotient of output current and input voltage, or of output voltage and input current. is constant aromas v 1n the pass band. although subieet to phase shin.

The constant value of the quotient is the midband impedance Rn or its reciprocal G. These relations follow from the conservation of power as the wave travels through the nlter.

In Fig-7b, the essential property of the fourterminai network is its transfer ratio.

The same transfer' ratio is retained in Fig. 'lc

in which the order of components is reversed:

fr. rfi' W In Fig. Bb, the essential property of the iilter is its transfer ratio,

` E, 11E. Y Ta?? 5) which is retained in Fig. 8o:

.lggllfgffn (45) By way of summary, Figs. Sri-8c, inclusive.

show two types of two-terminal networks and eight types of four-terminal networks. the latter including four permutations of input and output circuits of the two kinds, that is. one kind having shunt susceptance and one kind having series reactance, each permutation having two types depending on whether the dead-end filter is on the input or output side. In the low-pass illter examples shown, the susceptance is in the shunt capacitance of a current-regulated generator or a voltage-responsive load. while the reactance is in the series inductance of a voltage-regulated generator or a current-responsive load.

The above principles may be applied in proportioning a dead-end illter of the band-pass type and Fig. 9 is given by way of example of this type of filter. It will be seen that the band-pass filter ot Fig. 9 corresponds closely to the lo1w-pass lter of Fig. 8c: the principal difference being that the condensers Cm' and Cm" are effectively tuned by inductance elements L.' and In". re

across the input or impedance terminals oi' the lter of Fig. 3. may likewise be utilised to take into account shunt conductance or series resistance in other figures as follows: shunt conductance across the impedance terminals of Figs. 5a. 5b. 5c and 7a, 7b, 7c, these being the input terminals of Figs. 5a, 5b, 7a, and 7b and the out put terminals of Figs. 5c and 7c: 'series resistance between the admittance terminals of Pigs. 6a, 6b.

6c and 8a, 8b. 8c, these being the input terminals of Figs. 6a, 6b. 8a, and '8b and the output terminals of Figs. 6c and Bc. The resistance or conductance may include dissipation in the filter elements. per se, or in the associated circuits. either inherent or intentionally added. Y

Each oi Figs. 10a-10e, inclusive, shows a dlnerent four-terminal arrangement embodying the above principles in several different practical forms of low-pass four-terminal networks. The

terminal circuits are indicated in the drawings. The constant-lc and m-derived filter sections or half-sections are denoted k and m, respectively. The dead-end filter of Fig. 10a comprises confluent filter sections including,` in the order named, a constant-k section, an m-derived halfsection, and the terminating resistor Ro. The dead-end filter of Fig. 10b comprises confluent filter sections including, in the order named, a constant-k section, a constant-k half-section. an m-derived half-section, and the terminating resistor Ro. The dead-end filter of Fig. 10c comprises confiuent filter sections including, in the order named, two constant-lc sections, an m-derlved half-section, and the terminating resistor R0. The dead-end filter of Fig. 10d comprises confluent filter sections including, in the order named. an m-derlved section, an m-derived halfsection, and the terminating resistor Ro. The dead-end filter of Fig. 10e comprises confluent filter sections including, in the order named. a constant-lc half-section, an 11n-derived section, a constant-k half-section, a constant-k whole section, an m-derived half-section, and the terminating resistor Rn. In view of the reciprocal symmetry of the four-terminal networks shown in Figs. 10a-10e, inclusive. it will be understood that each of the terminal circuits indicated in the drawings can be either an input oran output circuit.

Fig. 1i shows, by way of example, a fourtermlnal band-pass network comprising a shunt capacitance and shunt inductance across the terminal circuits thereof. The low-pass filter of Fig. 10c may be converted into the band-pass filter of Fig. 11 by utilizing the principles outlined above to convert the low-pass filter of Fig. 8c to the band-pass filter of Fig. 9. The bandpass dead-end filter of Fig. l1 comprises, in the order named, a modified constant-k section of which capacitances Cm and Cm' are circuit elements, an m-derived half-section, and the terminating resistor Ra It will thus be seen that, by making n unity in the above' equations, the dead-end filters of the invention are effective to provide a uniform impedance across the terminal circuits of the filter: that is, maximum impedance across the terminals, a filter of the invention comprising shunt susceptance effectively across its terminals, and minimum impedance or maximum admittance between terminals comprising inductance effectively in series therewith. If amplitude correction is required between the input current or voltage and the output current or voltage of the terminal circuits involved, it can be secured by making n different from unity. Ii' phase correction is required between the input and output currents of voltages, phase-correcting networks may be inserted in the active part of the filter. An example of a low-pass filter in which phase correction is provided is found in the circuit of.' Fig. 10e, wherein the m-derived filter section denoted m" in the drawings may be designed for m"" 1, involving negative mutual inductance.

As illustrative of the practical applications of the above-described networks, the following list includes various types of wide band networks and some of the uses to which they are adapted. The dead-end filter of the invention may be on the input or the output side. In this list, shunt capacitance is denoted by (C); series lnductance is denoted by (L); and the combination of both. in series or parallel, is denoted as (CL). Each of these elements may be included in the filter design.

TnLnvisxoN Video frequency (low-pasa) Camera tube (C) to shielded cable (C) in amplifier grid` (C).

Amplifier anode (C) to condenser (C to ground) to amplifier grid (C).

Amplifier anode (C) to shielded cable (C) to ampiiner grid (C).

Amplifier anode (C) to shielded cable (C) to picture-tube grid (C).

Video-Signal translator (band-pass) Amplifier anode (C) to amplifier grid (C).

Amplifier anode (C) to shielded line to lowlmpedance antenna (CL).

Amplifier anode (C) to shielded line to highimpedance antenna (CL), the limiting factor being shunt susceptance.

Low-impedance antenna (CL), the limiting factor being series reactance, to shielded line to amplifier grid (C).

High-impedance antenna (CL), the limiting factor being shunt susceptance. to shielded line to amplifier grid (C).

Scanning (low-pass) Amplifier anode (C) to defiecting plates (C). Amplifier anode (C) to defiecting coils (CL), the limiting factor being series reactance.

Scanning (band-pass) Amplifier anode (C) to transformer (CL), the limiting factor being shunt susceptance, to deliecting plates.

Amplifier anode (C) to transformer (CL) to defiecting coils (CL), the limiting factor being series reactance.

SOUND Audio frequency (band-pass) Amplifier anode (C) to transformer (CL) to amplifier grid (C).

Moving coil (L) microphone or phonograph pick-up to transformer (CL) to amplifier grid (C).

Amplifier anode (C) to transformer (CL) to moving coll (L) loud-speaker or receiver.

Condenser (C) microphone or phonograph pick-up to transformer (CL) to amplifier grid (C).

Amplifier anode (C) to transformer (CL) to condenser (C) loud-speaker or receiver.

Each of Figs. 12-14, inclusive, shows an actual circuit arrangement utilizing the principles outlined above. In Fig. i2 there are shown three vacuum tubes 2|), 2|, and 22 included in succeeding stages of a vacuum-tube amplifier and coupled in cascade by means of filter circuits embodying the present invention. 'I'he output circuit of vacuum tube 2D is coupled to the input circuit of vacuum tube 2| by means of band-pass filter 23, in which the shunt capacitive filter elements 2l and 25 are comprised mainly of the inherent output capacitance of tube 20 and input capacitance of tube 2|, respectively. Similarly, the output circuit of vacuum tube 2i is coupled to the input circuit of vacuum tube 22 by a filter 26 in which the shunt capacitive filter elements 21 and 2l are comprised mainly of thel inherent output capacitance of tube 2| and input capacitance of tube 2| and input capacitance of tube 22, respectively.

It will be seen that the filter 2l corresponds in type to that shown in Fig. 10a, certain of the adjacent capacitance elements having been combined into single elements. Thus, the condenser 5 2| of Fig, 12 corresponds, in eiIect, to both of condensers Cn and Cm of Fig. a and condenser 28 corresponds to condensers Cm and Cm". Resistor 23' of Fig. 12 corresponds to terminating resistor R0 of Fig. 10a.

lo Filter 28 is similar to filter 23, except that the input and output terminals have been reversed and the addition of grid-leak resistor 28 makes it necessary to compute the constants of the filter using the parameter n' to take into account shunt conductance across a terminal circuit of the filter. 'I'he coupling circuits 28 and 28 may have different impedance-frequency characteristics over a wide range oi' frequencies and the constants of the filters may be so proportioned as to make these characteristics complementary over the frequency band, giving nearly uniform response over the pass band of the amplifier.

The filters 23 and 26 may be proportioned in accordance with the relationships expressed in Equation (i5) which reduce to the following expressions, the subscripts (1) referring to the filter 23 and the subscripts (2) to the filter 28, the other parameters utilized in the expressions having the denitions given above:

m which is nearly uniform because the :ci term is small over at least the greater portion of the pass band. The upward trend of the impedance characteristic toward the cutoff frequency of filters of the invention, in which n is different from 55 unity, may be utilized to compensate for filter attenuation in the circuit of Fig. 12. If the parameters n1 and nz are both unity, each of filters 22 and 26 has a uniform impedance over the pass bands. As examples of values of m, relating to m impedance characteristics of filter 2l having an upward trend in the pass band, and of nz, relating to complementary impedance characteristics of filter 2G, having a downward trend in the pass band, by use of which the impedances of the two lters vary in a complementary manner over the pass band, so that an approximately uniform overall response is obtained from the amplifier of Fig. 12, the circuit constants may be proportioned o according to the following relative parameters:

Iubes 2l and 2l may be relatively small. thus having relatively small electrode capacitances, and the tube 22 may be relatively large, thus having a relatively large input electrode capacitance. Attention is called to the fact that, with the 5 numerical values given above for parameters ni and ns, filter 28 may include a shunt capacitance 2l. which comprises the input capacitance of tube 22. which is materially greater than the shunt capacitance 21.fwhich comprises the output ca- 1o pacitance of tube 2t.

Attention is also directed to the fact that the resistance 2l' with nlter 2l may be taken into account and that the iilter 28 may be proportioned in accordance with the curves ot Fig. 4 and Equa- 15 tions (22)-(35), inclusive, so that filter 28 has a substantially uniform variation of impedance over the frequency range of the amplifier. The following parameters may be selected for such a filter: gg

In Fig. 13, thereis shown another adaptation of a filter designed in accordance with the invention, as a band-pass coupling system between two ampiiner tubes ll and 2i in which nearly the ideal maximum impedance is obtained in the coupling filter I2 over the pass band of the amplifier. This is an example of an application of the two-terminal network of the invention, the inductance a elements of the nlter being replaced by transformers 3l and 34. The nlter may be designed to compensate for resistance #l eiectively across the terminal circuit' of the iiiter 82. This resistance may be comprised in whole. or in part, of the inherent resistance of the primary circuit of transformer Il, which may be appreciable if the pass band of the ampliiier is narrow and the transformer Il is built very small in order to minimize its inherent capacitance. The other 40 circuit elements of the filter are then proportioned in accordance with the principles outlined above, particularly Equations (22)-(35), inclusive, to maintain subtantialiy uniform impedance over the pass band in the presence of shunt conductance, as indicated by the curves of Fig. 4.

In Fig. 14 there is shown a dead-end filter designed in accordance with the invention for coupling a push-pull power ampliiier comprising tubes 4I) and 4| to an antenna, the reactive constants 50 of which are represented by the elements within the dotted line l2. Tile antenna is assumed to be resonant in the middle of the pass band by its series inductance and capacitance, represented respectively by inductances I2 and It and con- 55 densers Il and 48. The shunt capacitance at the antenna terminals may also be included in the nlter design, if appreciable. as part of condenser 4 1. The antenna may be a balanced doublet. The radiation resistance represented by resistor 88 involves the parameter n' of the above expressions. The value of n must be comparable with unity if a compromise is desired between efiiciency of power radiation and tolerance of antenna reactance. If n' is equal to unity, the 65 reiiection of power at the antenna end is prevented in the middle of the frequency band. This is desirable if the carrier, or at least most of the signal energy, is concentrated in the middle of the frequency band.

The output capacitance of the stage of pushpull ampiincation comprising tubes Il) and Il is represented by condenser 4l, one of the circuit elements of the coupling' lter. Transformers I9, Il, il, I2, and Il are utilized to replace inductance elements of the nlter of the invention in a conventional manner. The coupling system of the circuit of Fig. 14 corresponds to the general type shown 'in Fig. 0c in that the input circuit is across shunt susceptance (capacitance 40) and the output circuit has in series therewith inductances I3, Il and conductance Il. The prototype of the circuit of Fig. 14, comprising individual illter sections in which the inductances have not been replaced by transformers, is a dead-end filter comprising, in the order named, a terminating resistor at the dead end which is the full equivalent of resistors Il. Il, an m-derived half-section the image impedance of which matches the resistance oi' the terminating rcsistor over the pass band, the input terminals across which capacitance Il is coupled, a conetant-Ic section, a second m-derived halt-section, a third m-derived half-section, a constant-lc whole section, a constant-la half-section, and the output terminals in series with which are the equivalent elements of the antenna comprising inductances 43. M, capacitances It, 46 and the conductance represented by resistor l1. I'he coupling filter utilized in Fig. 14 thus provides substantially uniform transmission from a power amplifier with shunt susceptance across its output terminals to an antenna having effective series reactance.

It will be understood that in the design of the dead-end filters of the invention. the preferred value of m is of the order of 0.6. Values of m between the limits of 0.5 to 0.7 result in a matching of the image impedance of the m-derived iilter section with the terminating resistor R at two points in a low-pass band or four points in a band-pass filter. Filters having an m-derlved termination with a value of m more than 0.7 cannot match the terminal resistor R0 at more than one point in a low-pass band or two points in a band-pass filter. Each additional m-derivation included in the illter termination makes it possible to match the image impedance with the terminal resistor at one additional point in a low-pass band or two additional points in a bandpass iilter.

While there have been described what are at present considered to be the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modiilcations may be made therein without departing from the invention, and it is, therefore, aimed inthe appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A signal-translating system for operation over a range of frequencies comprising one or more pairs of terminals between one pair of which there is eil'ectively substantial reactance and substantial resistance both tending to limit the response of said system over said range. a dead-end filter having a predetermined image impedance over said range coupled to said one of said pairs of terminals, said illter comprising only a .part of said reactance as a terminal midelement of said filter, and an impedance termination coupled to the dead end of said illter proportioned substantially to match the image impedance of said illter over said range, the reactive constant of said dead-end iilter being so proportioned relative to said reactance, said resistance, and the operating frequency range that the impedance between said one vi wld Pairs af terminals over said range is substantially uniform and approximately the limiting value that can be maintained between said one pair of terminais over said range.

2. A signal-translating system for operation over a wide range of frequencies comprising one or more pairs o! terminals in series with one pair of which there is eilectiveiy substantial inductance and substantial resistance both tending to limit the response of said system over said range, a dead-end lter having a predetermined image impedance over said range coupled to said one of said pairs of terminals, said illter comprising only a part oi' said inductance as a terminal midseries element of said lter, and an impedance termination coupled to the dead end of said filter proportioned substantially to match the image impedance of said filter over said range, the reactive constants of said dead-end illter being so proportioned relative to said inductance, said resistance, and the operating frequency range that the admittance between said terminals is substantially constant and approximately the maximum that can be maintained between said one pair of terminals over said range.

3. A signal-translating system for operation` over a wide range of frequencies comprising one or more pairs of terminals across one pair of which there is eiectively substantial capacitance and substantial conductance both tending to limit the response of said system over said range, a dead-end filter having a predetermined impedance over said range coupled to said one of said pairs of terminals, said illter comprising only a part oi said capacitance as a terminal mid-shunt element of said niter, and an impedance termination coupled to the dead end of said illter proportioned substantially to match the image impedance of said flitsr over said range, the reactive constants of said dead-end iter being so proportioned relative to said capacitance, said conductance, and the operating frequency range that the impedance across said one pair of terminals is substantially constant and approximately the maximum that can be maintained across said one pair oi' terminals over said range.

4. A signal-translating system for operation over a wide range oi frequencies comprising two or more pairs of terminals across a rst pair of which there is eiectively capacitance and conductance and across a second pair of which there is -eiectively capacitance, said capacitances and said conductance tending to limit the response of said system over said range, a dead-end iliter having a predetermined image impedance over said range coupled to said iirst pair of terminals, said iter comprising only a part of the impedance associated with said rst pair of terminals as a terminal mid-shunt element of said iilter and comprising the impedance associated with said second pair of said terminals as a full-shunt element of said lter, and an impedance termination coupled to the dead end of said illter proportioned substantially to match the image impedance of said filter over said range, the reactive constants of said dead-end filter being so proportioned relative to the impedance across said iirst pair of terminals and the operating frequency range that the impedance across said first pair of temilnals is substantially constant and approximately the maximum that can be maintained across said first pair over said range.

5. A signal-translating system for operation over a Wide range oifrequencies comprising two or more pairs of terminals across a first pair of which there is effectively capacitance and conductance and across a second pair of which there is effectively capacitance, said capacitances and said conductance tending to limit the response of said system over said range, a deadend filter having a predetermined image impedance over said range coupled to said first pair of terminals, said filter comprising only a part of the capacitance across said first pair of terminals as a terminal mid-shunt element of said filter and comprising the capacitance across said second pair of terminals as a full-shunt element of said filter, and an impedance termination coupled to the dead end of said filter proportioned substantially to match the image impedance of said filter over said range, the reactive constants of said filter being proportioned in accordance with the expression n-n=1 where the parameters have the significance given in the specification.

6. A signal-translating system for operation over a. wide range of frequencies comprising one or more pairs of terminals in series with a first pair of which there is effectively substantial inductance and substantial resistance and in series with a second pair of which there is effectively substantial inductance, said elements tending to limit the response of said system over said range. a dead-end filter having a predetermined image impedance over said range coupled to said first pair of terminals comprising only a part of the impedance associated with said first pair of terminals as a terminal mid-series element of said filter and comprising the impedance associated with said second pair of terminals as a full-series element of said filter, and an impedance termination coupled to the dead end of said filter proportioned substantially to match the image impedance of said filter over said range, the reactive constants of said filter being so proportioned with respect to the impedance associated with said first pair of terminals and the operating irequency range that the admittance between said first pair of terminals is substantially constant and approximately the maximum that can be maintained between said first pair of terminals over said range.

7. A signal-translating system for operation over a wide range of frequencies comprising two or more pairs of terminals in series with a first pair of which there is effectively substantial inductance and substantial resistance and across a second pair of' which there is effectively substantial capacitance, said inductance, resistance, and capacitance tending to limit the response of said system over said range, a dead-end filter having a predetermined image impedance over said range coupled to said rst pair of terminals, said filter comprising only a part ol' the impedance associated with said first pair of terminals as a terminal mid-series element of said filter and utilizing the impedance associated with said second pair of' terminals as a full-shunt element of said filter, and an impedance termination coupled to the dead end of said filter proportioned substantially to match the image impedance of said filter over said range, the reactive constants of said dead-end filter being so proportioned relative to said impedance associated with said first pair of terminals and the operating frequency range that the admittance between said first pair of terminals over said range is substantially constant and approximately the maximum that can be maintained between said lSiS Pair 0f' terminals over said range.

8. A signal-translating system for operation over a wide range oi' frequencies comprising two or more pairs of terminals across a first pair of which there is effectively substantial capacitance and substantial conductance and in series with a second pair oi' which there is effectively substantial inductance, said capacitance, conductance, and inductance tending to limit the response of said system over said range. a dead-end filter having a predetermined image impedance over said range coupled to said first pair of terminals comprising only a part of the capacitance associated with said first pair of terminals as a terminal mid-shunt element of said filter and comprising the impedance associated with said second pair of terminals as a full-series element of said filter, and an impedance termination coupled to the dead end of said filter proportioned substantially to match the image impedance ofsaid filter over said range, the reactive constants of said filter being so proportioned relative to the impedance associated with said first pair of terminals and the operating frequency range that the impedance across said first pair of terminals over said range is substantially constant and approximately the maximum impedance which can be maintained across said terminals over said range.

9. A signal-translating system for operating over a wide range of frequencies comprising two component networks coupled in cascade, each of said networks comprising a pair of terminals between which there is effectively reactance tending to limit the response of said system over said range, two dead-end filters having the same cutofi frequencies and each having a predetermined image impedance over said range coupled respectively to said pairs of terminals, each of said filters comprising only a part of the reactance coupled to its respective terminals as a terminal mid-element of the filter, and an impedance termination coupled to the dead end of each of said filters proportioned substantially to match the image impedance of the filter over said range, the reactive constants of said dead-end filters being so proportioned relative to said terminal reactance and the operating frequency range that the mean value of impedance between said pairs of terminals is substantially the limiting value of impedance which can be maintained between said terminals over said range, said impedances varying in a complementary manner over said range. whereby a predetermined response is obtained from said system over said frequency range.

10. A signal-translating system for operation over a wide range of frequencies comprising two component networks coupled in cascade. each of said networks comprising a pair of terminals between which there is eii'ectively reactance tending to limit the response of said system over said range, two dead-end filters having the same cutoff frequencies and each having a predetermined image impedance over said range coupled respectively to said pairs of terminals. each of said filters comprising only a part of the reactance coupled to its respective terminals as a terminal mid-element at the active end of the filter, and an impedance termination coupled to the dead end of each of said filters proportioned substantially to match the image impedance of the filter over said range, the reactive constants of said dead-end filters being proportioned in accordance with the expression nF4-M222 where nl 1S a parameter of one of said filters and ns a parameter of the other of said filters, said parameters having the significance defined in the specification.

11. A signal-translating system for operation over a wide range of frequencies for coupling a first terminal circuit comprising inherent shunt capacitance to a series-resonant terminal circuit including series resistance, said capacitance and the elements of said series-tuned circuit tending to limit the response of said system over said range, a dead-end band-pass filter having a predetermined image impedance over said range coupled to said terminal circuits comprising only a part of the reactive elements of said seriestuned circuit as a terminal mid-series arm of said filter and comprising said capacitance as a full-shunt element of said filter, and an impedance termination coupled to the dead end of said filter proportioned substantially to match the image impedance of said filter over said range, the reactive constants of said lter being so proportioned with respect to the reactive constants of said series-tuned circuit and the operating frequency range that the admittance through said series-tuned circuit and said filter is substantially constant and approximately the maximum that can be maintained over said range.

12. A signal-translating system for operation over a wide range of frequencies for coupling the output circuit of a vacuum-tube amplifier having inherent output capacitance to a seriesresonant terminal circuit including series resistance, said capacitance and the elements of said series-tuned circuit tending to limit the response of said system over said range. a dead-end bandpass filter having a predetermined image impedance over said range coupled to said terminal circuit and comprising only a part of the reactive elements thereof as a terminal mid-series element of said filter and comprising said capacitance as a full-shunt element of said filter, and an impedance termination coupled to the dead end of said filter proportioned substantially to match the image impedance of said filter over said range. the reactive constants of said filter being so proportioned with respect to the reactive constants of said series-tuned circuit and the operating frequency range that the admittance through said series-tuned circuit and the filter is substantially constant and approximately the maximum that can be maintained over said range.

13. A signal-translating system for operation over a wide range of frequencies comprising a first terminal circuit having inherent shunt capacitance, a uniform impedance transmission line and a series-resonant terminal 'circuit including series resistance, said capacitance and the elements of said series-tuned circuit tending to linut the response of said system over said range, a dead-end filter coupled between said first terminal circuit and one end of said transmission line and comprising said capacitance as a full-shunt element of said filter, and an impedance termination coupled to the dead end of said filter proportioned substantially to match the image impedance of said filter over said range, a second filter coupled between the other end of said transmission line and said seriestuned circuit comprising only a part of said reactive elements of said series-tuned circuit as a terminal mid-series element thereof, the reactive constants of said filters being proportioned relatlve to the constants of said tuned circuit and the operating frequency range, so that uniform admittance is maintained through said tuned circuit and said second filter over said range.

14. A signal-translating system for operation over a wide range of frequencies comprising a vacuum-tube amplifier having inherent output capacitance, a uniform impedance transmission line and a series-resonant output circuit including series resistance, said capacitance and the elements of said series-resonant circuit tending to limit the response of said system over said range, a dead-end filter coupled between the output circuit of said amplifier and one end of said transmission line and comprising said capacitance as a full-shunt element of said filter, an impedance termination coupled to the dead end of said filter proportioned substantially to match' the image impedance of said filter over said range, a second filter coupled between the other end of said transmission line and said seriestuned circuit comprising only a part of the reactive elements of said series-tuned circuit as a terminal mid-series element thereof, the reactive constants of said filters being proportioned relative to the constants of said tuned circuit and the operating frequency range so that uniform admittance is maintained through said tuned circuit and said second filter over said range.

15. A signal-translating system for operation over a wide range of frequencies comprising a first terminal circuit having inherent shunt capacitance, a uniform impedance transmission line and a series-resonant terminal circuit, said capacitance and the elements of said series-resonant circuit tending to limit the response oi' said system over said range, a dead-end filter coupled between said first terminal circuit and one end of said transmission line and comprising said capacitance as a full-shunt element of said filter. and an impedance termination coupied to the dead end of said lter proportioned substantially to match the image impedance of said filter over said range, a second filter cou pled to the other end of said transmission line and said series-tuned circuit comprising only a part of the reactive elements of said series-tuned circuit as a terminal mid-series element thereof. the reactive constants of said filters being proportioned relative to the constants of said tuned circuit and the operating frequency range so that the response of one of said filters is complementary to that of the other over said range and a uniform response is maintained through said system over said range.

16. A signal-translating system for operation over a wide range of frequencies comprising two r more component networks coupled in cascade, each of said networks comprising a pair of terminals across which there is effectively substantial capacitance tending to limit the response of said system over said range, a. dead-end filter for each of said networks having a predetermined image impedance over said range and coupled to the respective pairs of terminals, said filters having the same cutoff frequencies and each comprising only a part of the capacitance across which the filter is coupled as a terminal mid-shunt element of the filter, and an impedance termination coupled to the dead end of each filter proportioned substantially to match the image impedance of the filter over said range, the reactive constants of said filter being so proportioned relative to said capacltances and the operating frequency that the mean value of impedance across each of said pairs of terminals is substantially the maximum that can be malntained across said terminals over said range. said impedances across said terminals varying in a complementary manner over said range to produce a substantially uniform response in said system over said range.

only a part of the capacitance of said pair of terminals as a terminal mid-shunt element oi said filter, and an impedance termination coupled to the dead-end of said filter proportioned substantially to match the image impedance oi' said filter over said range, the reactive constants oi' said iliter being proportioned in accordance with the expression where the parameters have a significance given in the speoiiication.

A HAROLD A. WHEELER.

Certiilcate of Correction Patent No. 2,167,134.

July 25, 1939.

l HAROLD A. WHEELER It is hereby certified that errors appear in the irinted specification of the above numbered patent requiring correction as folio age 3, second column, line 38,

for Z/p read Z/R; line 43, for b=1r2 read b=1r/2; line 55, for +1 read il;

page 4, first column, line 2, for x2 read 1r/2 28, for nl read n' page 5, second column, read R.,w; page 7, first column,

Patent Office.

and second column, line 32, Equation hnes 41 and 44, Equation 37, for ROM line 59, for of read or' page 9, first column, lines 35 and 39, for R read R; and that the said Letters l these corrections therein that the same may conform to stent should be read with the record of the case in the Signed and sealed this 10th day of October, A. D. 1939.

[nml

HENRY VAN ARSDALE,

Acting Commissioner of Patents.

substantially the maximum that can be malntained across said terminals over said range. said impedances across said terminals varying in a complementary manner over said range to produce a substantially uniform response in said system over said range.

only a part of the capacitance of said pair of terminals as a terminal mid-shunt element oi said filter, and an impedance termination coupled to the dead-end of said filter proportioned substantially to match the image impedance oi' said filter over said range, the reactive constants oi' said iliter being proportioned in accordance with the expression where the parameters have a significance given in the speoiiication.

A HAROLD A. WHEELER.

Certiilcate of Correction Patent No. 2,167,134.

July 25, 1939.

l HAROLD A. WHEELER It is hereby certified that errors appear in the irinted specification of the above numbered patent requiring correction as folio age 3, second column, line 38,

for Z/p read Z/R; line 43, for b=1r2 read b=1r/2; line 55, for +1 read il;

page 4, first column, line 2, for x2 read 1r/2 28, for nl read n' page 5, second column, read R.,w; page 7, first column,

Patent Office.

and second column, line 32, Equation hnes 41 and 44, Equation 37, for ROM line 59, for of read or' page 9, first column, lines 35 and 39, for R read R; and that the said Letters l these corrections therein that the same may conform to stent should be read with the record of the case in the Signed and sealed this 10th day of October, A. D. 1939.

[nml

HENRY VAN ARSDALE,

Acting Commissioner of Patents. 

